Integrated circuits (IC) are the cornerstone of the information age and the foundation of today's information technology industries. The integrated circuit, a.k.a. “chip” or “microchip,” is a set of interconnected electronic components, such as transistors, capacitors, and resistors, which are etched or imprinted onto a tiny wafer of semiconducting material, such as silicon or germanium. Integrated circuits take on various forms including, as some non-limiting examples, microprocessors, amplifiers, Flash memories, application specific integrated circuits (ASICs), static random access memories (SRAMs), digital signal processors (DSPs), dynamic random access memories (DRAMs), erasable programmable read only memories (EPROMs), and programmable logic. Integrated circuits are used in innumerable products, including personal computers, laptop and tablet computers, smartphones, flat-screen televisions, medical instruments, telecommunication and networking equipment, airplanes, watercraft and automobiles.
Advances in integrated circuit technology and microchip manufacturing have led to a steady decrease in chip size and an increase in circuit density and circuit performance. The scale of semiconductor integration has advanced to the point where a single semiconductor chip can hold tens of millions to over a billion devices in a space smaller than a U.S. penny. Moreover, the width of each conducting line in a modern microchip can be made as small as a fraction of a nanometer. The operating speed and overall performance of a semiconductor chip (e.g., clock speed and signal net switching speeds) has concomitantly increased with the level of integration. To keep pace with increases in on-chip circuit switching frequency and circuit density, semiconductor packages currently offer higher pin counts, greater power dissipation, more protection, and higher speeds than packages of just a few years ago.
Conventional microchips are generally rigid structures that are not designed to be bent or stretched during normal operating conditions. In addition, IC's are typically mounted on a printed circuit board (PCB) that is as thick or thicker than the IC and similarly rigid. Processes using thick and rigid printed circuit boards are generally incompatible with chips that are thinned or intended for applications requiring elasticity. Consequently, many schemes have been proposed for embedding microchips on or in a flexible polymeric substrate. Flexible electronic circuitry employing an elastic substrate material allows the IC to be adapted into innumerable shapes. This, in turn, enables many useful device configurations not otherwise possible with rigid silicon-based electronic devices. However, some flexible electronic circuit designs are unable to sufficiently conform to their surroundings because the interconnecting components are unable to flex in response to conformation changes. Such flexible circuit configurations are prone to damage, electronic degradation, and can be unreliable under rigorous use scenarios.
Many flexible circuits now employ stretchable and bendable interconnects that remain intact while the system stretches and bends. An “interconnect” in integrated circuits electrically couples the IC modules to distribute clock and other signals and provide power/ground throughout the electrical system. Some flexible interconnects capable of bending and elasticity comprise metal segments that are embedded in an elastomer. For example, one known approach includes using micro-fabricated tortuous wires encased in a silicone elastomer to enable significant linear strain while maintaining conductivity. Elastically stretchable metal interconnects, however, tend to experience an increase in resistance with mechanical strain. There is therefore a continuing need for improved stretchable interconnects having improved stretchability, electrical conductivity, and related properties for rapid and reliable manufacture of flexible electronic circuitry in a variety of different configurations.